1. Field of the Invention
The present invention is in the field of rotary seals for low pressure applications. A particular area of utility for the seal of the instant invention is to isolate the interior of a mixing container, feed auger assembly or the like from the motor or other means for applying rotary power therefor.
2. The Prior Art
Numerous means have been suggested for forming rotary seals for a drive shaft extending through the wall or casing of a container or feed device to prevent the escape of dust, pulverulent material or the like.
In accordance with one form of seal, waste or packing material which may be suitably impregnated with a lubricant is mounted in a gland extending through the wall of the container. The effectiveness of the seal against the passage of detritus is directly proportional to the forces with which the waste material is compressed against the periphery of the shaft. Such devices are disadvantageous on many counts, including extremely high starting torque, being six to seven times the running torque. Additionally, such rotary seals must be frequently adjusted to compensate for wear and maintain the pressure of the packing against the shaft within a predetermined range. Further, lubrication on the packing often contaminates the material within the container and entraps material which, where the same is abrasive, results in accelerated wear on the shaft.
It is, for instance, necessary to readjust a standard packing gland, in a typical application, after each one hundred to two hundred hours of use, and a complete change of packing must be effected about every three months. Naturally, the frequency of adjustment and replacement of packing will vary from installation to installation, depending in a measure on the nature of the pulverulent material with which the rotary seal is contacted.
A further drawback of conventional low pressure rotary seals lies in their inability to compensate for eccentricities or axial misalignments between the drive shaft and other components, and where such inaccuracies exist, the starting torque and wear rates are dramatically increased.